1. Field of the Invention
This invention generally relates to a bicycle crank assembly. More specifically, the present invention relates to a bicycle crank assembly that includes a axial play adjustment function for adjusting axial play in a crank axle.
2. Background Information
Bicycling is becoming an increasingly more popular form of recreation as well as a means of transportation. Moreover, bicycling has become a very popular competitive sport for both amateurs and professionals. Whether the bicycle is used for recreation, transportation or competition, the bicycle industry is constantly improving the various components of the bicycle. One component that has been extensively redesigned is the bicycle drive train.
Typically, the drive train of a bicycle is a chain drive that includes one or more front sprockets and one or more rear sprockets that are connected by a chain. The front sprockets are non-rotatably attached to a crank axle that is rotatably supported in a hanger tube of a bicycle frame. The crank axle also has a crank arm non-rotatably mounted on each end with each crank arm having a pedal attached thereto. Sometimes the right side crank arm has a sprocket mounting part for non-rotatably attaching the front sprockets thereon to form a bicycle crank assembly. In this type of bicycle crank assembly, the right side gear crank is conventionally crimp-fastened to the crank axle. A conventional left side crank arm has a crank axle mounting part with a crank axle mounting hole for the left end of the crank axle. A crank axle mounting part also has a slit extending radially from the crank axle mounting hole and two clamping bolts for narrowing the slit to clamp the left end of the crank axle in the crank axle mounting hole. Furthermore, the left side crank assembly is often fixed to the crank axle by a fixed bolt that screws into the left inner circumferential surface of the crank axle. Some examples of conventional crank assemblies are disclosed in U.S. Patent Publication No. 2006/0101941 (assigned to Shimano Inc.), U.S. Patent Publication No. 2006/0112780 (assigned to Shimano Inc.) and U.S. Patent Publication No. 2007/0062328 (assigned to Shimano Inc.).
In the case of a tandem bicycle, the tandem bicycle typically has a front crankset, a timing chain, a rear crankset and a drive chain. The timing chain and the drive chain are connected in series. The front crankset has a front crank axle with a front bicycle crank assembly mounted on a left end of the front crank axle and a crank arm mounted on the right side of the front crank axle. The rear crankset has a rear crank axle with a rear bicycle crank assembly mounted on each end of the rear crank axle. The timing chain connects the front bicycle crank assembly with the rear bicycle crank assembly mounted on the left side of the rear crank axle. The drive chain connects the rear bicycle crank assembly mounted on the right side of the rear crank axle to gears mounted to the rear wheel. This configuration is called a crossover rear drive. The front crankset typically has only one chain ring or sprocket. The rear crankset typically has many chain rings or sprockets, sometimes on both sides. On a tandem bicycle where the pedaling is designed to be in sync, both the front and rear cranksets will use a chain ring for the timing chain of the same size. The chain rings of the right side rear bicycle crank assembly can be a single gear or multiple gears that use a derailleur.
In the case of a tandem bicycle, typically no adjustment mechanism is provided for adjusting axial play in a conventional rear crank axle so that the crank axle rotates smoothly without bearing movement in the axial direction after both of the rear bicycle crank assemblies are mounted to the rear crank axle. Therefore, in many cases, adjustment of axial play is accomplished during fixing of the rear bicycle crank assemblies to the rear crank axle using shims. In this case, the work of axial adjustment becomes complicated since removing one of the rear bicycle crank assembly must be repeated to add and subtract the shims when changing gap using shims during axial play adjustment.